NAME
HTTP::LRDD - link-based resource descriptor discovery
SYNOPSIS
use HTTP::LRDD;
my $lrdd = HTTP::LRDD->new;
my @descriptors = $lrdd->discover($resource);
foreach my $descriptor (@descriptors)
{
my $description = $lrdd->parse($descriptor);
# $description is an RDF::Trine::Model
}
DESCRIPTION
Note: the LRDD specification has ceased to be, with some parts being
merged into the host-meta Internet Draft. This CPAN module will go in
its own direction, bundling up best-practice techniques for discovering
links and descriptors for a given URI.
Import Routine
"use HTTP::LRDD (@predicates)"
When importing HTTP::LRDD, you can optionally provide a list of
predicate URIs (i.e. the URIs which rel values expand to). This may
also include IANA-registered link types, which are short tokens
rather than full URIs. If you do not provide a list of predicate
URIs, then a sensible default set is used.
Because this configuration is global in nature, it is not
recommended. It is better to supply a list of predicates to the
constructor instead, or rely on the defaults. This feature should be
regarded as deprecated.
Constructors
"HTTP::LRDD->new(@predicates)"
Create a new LRDD discovery object using the given predicate URIs.
If @predicates is omitted, then the predicates passed to the import
routine are used instead.
"HTTP::LRDD->new_strict"
Create a new LRDD discovery object using the 'describedby' and
'lrdd' IANA-registered predicates.
"HTTP::LRDD->new_default"
Create a new LRDD discovery object using the default set of
predicates ('describedby', 'lrdd', 'wdrs:describedby', 'xhv:meta'
and 'rdfs:seeAlso').
Public Methods
"$lrdd->discover($resource_uri)"
Discovers a descriptor for the given resource; or if called in a
list context, a list of descriptors.
A descriptor is a resource that provides a description for
something. So, if the given resource URI was the web address for an
image, then the descriptor might be the web address for a metadata
file about the image. If the given URI was an e-mail address, then
the descriptor might be a profile document for the person to whom
the address belongs.
The following sources are checked (in order) to find links to
descriptors.
* HTTP response headers ("Link" header; "303 See Other" status)
* HTTP response message (RDF or RDFa)
* https://HOSTNAME/.well-known/host-meta
* http://HOSTNAME/.well-known/host-meta
If none of the above is able to yield a link to a descriptor, then
the resource URI itself may be returned if it is in a
self-describing format (e.g. RDF).
There is no guaranteed file format for the descriptor, but it is
usually RDF, POWDER XML or XRD.
This method can also be called without an object (as a class method)
in which case, a temporary object is created automatically using
"new".
"$lrdd->parse($descriptor_uri)"
Parses a descriptor in XRD or RDF (RDF/XML, RDFa, Turtle, etc).
Returns an RDF::Trine::Model or undef if unable to process.
This method can also be called without an object (as a class method)
in which case, a temporary object is created automatically using
"new".
"$lrdd->process($resource_uri)"
Performs the equivalent of "discover" and "parse" in one easy step.
Calls "discover" in a non-list context, so only the first descriptor
is used.
"$lrdd->process_all($resource_uri)"
Performs the equivalent of "discover" and "parse" in one easy step.
Calls "discover" in a list context, so multiple descriptors are
combined into the resulting graph.
EXAMPLES
Discover the hub address (PubSubHubub) for a feed:
my $lrdd = HTTP::LRDD->new('hub');
my $hub = $lrdd->discover('http://example.net/feed.atom');
Discover an author link (rel="author") from an HTML page:
my $lrdd = HTTP::LRDD->new('author');
my $author = $lrdd->discover('http://example.com/page.html');
(For RDF people, you should note that rel="author" is not semantically
equivalent to the "foaf:maker" property but closer to the
"foaf:maker/foaf:homepage" SPARQL 1.1 property path - i.e. the
rel="author" link destination is not a URI for the author themselves,
but a page about the author.)
If that author resource is in a machine-readable format (e.g. RDF), then
parse the data:
my $author_data = $lrdd->parse($author);
Or, you can combine "discover" and "parse":
my $lrdd = HTTP::LRDD->new('author');
my $author_data = $lrdd->process('http://example.com/page.html');
Get metadata for an image:
my $lrdd = HTTP::LRDD->new;
my $data = $lrdd->process_all('http://example.org/flower.jpeg');
As we're not passing any arguments to the constructor, we can use a
shortcut:
my $data = HTTP::LRDD->process_all('http://example.org/flower.jpeg');
Find the title of the image:
use RDF::QueryX::Lazy;
my $image = q;
my $results = RDF::QueryX::Lazy
-> new("SELECT * WHERE { dc:title ?t }")
-> execute( HTTP::LRDD->process_all($image) );
BUGS
Please report any bugs to .
Note: many problems can stem from servers that send incorrect
"Content-Type" headers. If you send an XRD file as "text/html", then
this module will not guess what you're doing - it will assume the file
is really HTML, and inspect it for RDFa. For host-meta files, this
module is slightly more relaxed, as there's a strong assumption that
they are XRD... but YOU SHOULD NOT RELY ON THIS. If you're running a
server, use the correct media type.
SEE ALSO
HTTP::Link::Parser, XRD::Parser, XML::Atom::OWL WWW::Finger.
.
AUTHOR
Toby Inkster .
COPYRIGHT AND LICENCE
Copyright 2010-2012 Toby Inkster
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
DISCLAIMER OF WARRANTIES
THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.